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//-----------------------------------------------------------------------------
//
// Copyright (C) Microsoft Corporation. All Rights Reserved.
//
//-----------------------------------------------------------------------------
using System.Collections.Generic;
using Microsoft.Contracts;
namespace Microsoft.Boogie
{
public delegate System.Collections.IEnumerable/*<Node!>*/! Adjacency<T>(T! node);
// An SCC is a set of nodes
public sealed class SCC<Node> : ICollection<Node>
{
private IDictionary<Node,object>! nodesMap = new Dictionary<Node,object>();
private ICollection<Node>! nodes { get { return (!) nodesMap.Keys; } }
[Pure] [GlobalAccess(false)] [Escapes(true,false)]
System.Collections.IEnumerator! System.Collections.IEnumerable.GetEnumerator()
{
return ((System.Collections.IEnumerable)nodes).GetEnumerator();
}
[Pure] [GlobalAccess(false)] [Escapes(true,false)]
IEnumerator<Node>! IEnumerable<Node>.GetEnumerator()
{
return ((IEnumerable<Node>)nodes).GetEnumerator();
}
public int Count { get { return nodes.Count; } }
public bool IsReadOnly { get { return nodesMap.IsReadOnly; } }
public void Add(Node item) { nodesMap.Add(item,null); }
public void Clear() { nodesMap.Clear(); }
[Pure][Reads(ReadsAttribute.Reads.Owned)]
public bool Contains(Node item) { return nodesMap.ContainsKey(item); }
public void CopyTo(Node[]! array, int arrayIndex) { nodes.CopyTo(array, arrayIndex); }
public bool Remove(Node item) { return nodesMap.Remove(item); }
}
public sealed class StronglyConnectedComponents<Node> : IEnumerable<SCC<Node>!>
{
private readonly IDictionary<Node!,object>! graph;
private readonly Adjacency<Node>! preds;
private readonly Adjacency<Node>! succs;
private bool computed = false;
public bool Computed { get { return computed; } }
[NotDelayed]
public StronglyConnectedComponents(System.Collections.IEnumerable/*<Node!>*/! graph, Adjacency<Node>! preds, Adjacency<Node>! succs)
ensures !Computed;
{
IDictionary<Node!,object>! dict = new Dictionary<Node!,object>();
foreach (Node! n in graph) { dict.Add(n,null); }
this.graph = dict;
this.preds = preds;
this.succs = succs;
base();
}
[Pure] [GlobalAccess(false)] [Escapes(true,false)]
System.Collections.IEnumerator! System.Collections.IEnumerable.GetEnumerator()
{
return ((System.Collections.IEnumerable)sccs).GetEnumerator();
}
[Pure] [GlobalAccess(false)] [Escapes(true,false)]
IEnumerator<SCC<Node>!>! IEnumerable<SCC<Node>!>.GetEnumerator()
{
assume Computed;
return ((IEnumerable<SCC<Node>!>)sccs).GetEnumerator();
}
private readonly IList<SCC<Node>!>! sccs = new List<SCC<Node>!>();
public void Compute()
requires !Computed;
ensures Computed;
{
// Compute post times on graph with edges reversed
this.dfsNext = this.preds;
foreach (Node! n in (!)graph.Keys)
{
if (!seen.ContainsKey(n))
{
OrderNodes(n);
}
}
// Clear seen
seen.Clear();
// Compute SCCs
this.dfsNext = this.succs;
while (postOrder.Count > 0)
{
Node! n = postOrder.Pop();
if (!seen.ContainsKey(n))
{
SCC<Node>! curr = new SCC<Node>();
FindSCCs(n, curr);
sccs.Add(curr);
}
}
// Clear seen
seen.Clear();
this.computed = true;
}
private Adjacency<Node>/*?*/ dfsNext = null;
private readonly IDictionary<Node!,object>! seen = new Dictionary<Node!,object>();
private readonly Stack<Node!>! postOrder = new Stack<Node!>();
// DFS to order nodes by post times
private void OrderNodes(Node! node)
{
seen.Add(node,null);
assert dfsNext != null;
System.Collections.IEnumerable! nexts = dfsNext(node);
foreach (Node! n in nexts)
{
if (graph.ContainsKey(n) && !seen.ContainsKey(n)) { OrderNodes(n); }
}
postOrder.Push(node);
}
// DFS to compute SCCs
private void FindSCCs(Node! node, SCC<Node>! currSCC)
//modifies currSCC.*;
{
seen.Add(node,null);
currSCC.Add(node);
assert dfsNext != null;
System.Collections.IEnumerable! nexts = dfsNext(node);
foreach (Node! n in nexts)
{
if (graph.ContainsKey(n) && !seen.ContainsKey(n)) { FindSCCs(n,currSCC); }
}
}
[Pure][Reads(ReadsAttribute.Reads.Owned)]
public override string! ToString()
{
string outStr = "";
int i = 0;
foreach(ICollection<Node> component in this)
{
string! tmp = System.String.Format("\nComponent #{0} = ", i++);
outStr += tmp;
bool firstInRow = true;
foreach(Node b in component)
{
string! tmpComponent = System.String.Format("{0}{1}", firstInRow? "" : ", ", b);
outStr += tmpComponent;
firstInRow = false;
}
}
return outStr;
}
}
}
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